1. Field of the Invention
The present invention relates to a monoaxially elastic laminate film that can stretch elastically in a preferred stretching direction, and possesses a relatively fixed and non-elastic structure perpendicular to this stretching direction.
2. The Prior Art
Monoaxially elastic laminates are used, for example, for disposable hygiene products such as diapers and incontinence pads, for example in the elastic waistbands of these articles. See U.S. Pat. No. 4,681,580. For such uses, material in strips is required, which can stretch by two to several times its original length in the lengthwise direction, and which demonstrate a high level of shape stability in the direction perpendicular to it. The material is supposed to act as much as possible like conventional elastics, which are produced, in terms of textile technology, as knitted structures with latex braids knitted into them. Such elastics are described, for example, in H. Vavra, Grundlehre der Schneiderei [Principles of Tailoring], Verlag Otto Beyer, Leipzig, 1935, page 47.
A laminate film is known from DE 197 15 938 A1, which has a core layer made of a thermoplastic elastomer, and skin layers made of a brittle material. The elastic core is made sticky with tackifiers, for example. The skin layers, which are preferably applied to the core layer on both sides, consist of a thermoplastic plastic that becomes brittle when cured, and inorganic fillers to promote the brittleness of the material. With these measures, the laminate film is connected with a nonwoven fabric. The strips to be connected are passed to a pair of rollers and are exposed to pressure stress in the roller nip. Because of the pressure stress, the skin layer breaks down into fibers, and the nonwoven fabric is connected with the exposed sticky surface of the core layer. Neither the laminate film nor the laminate consisting of the laminate film and the nonwoven fabric demonstrate the properties of a conventional elastic that are required for the use described initially.
A fluffy laminate film is described in DE 195 26 044 A1, which has a core layer made of a thermoplastic elastomer and at least one skin layer co-extruded together with the core layer, made of a thermoplastic, stretchable plastic base substance, and additive particles heterogeneously bonded into it. After having been extruded, the laminate film is stretched in one or more axes, whereby the additive particles come loose from the plastic base substance that surrounds them, at their border regions, and they stand up to form a fluffy surface when the stretched laminate film relaxes. This film also does not demonstrate the properties of an elastic that possesses a high degree of elasticity in a preferred stretching direction and is stable in shape in the direction perpendicular to that.